Let's get this math done. We have 618 and we're going to multiply it by 21. This is the same as taking 618 and adding it to itself 21 times.
Step 1: 0 + 618 = 618
Step 2: 618 + 618 = 1236
Step 3: 1236 + 618 = 1854
Step 4: 1854 + 618 = 2472
Step 5: 2472 + 618 = 3090
Step 6: 3090 + 618 = 3708
Step 7: 3708 + 618 = 4326
Step 8: 4326 + 618 = 4944
Step 9: 4944 + 618 = 5562
Step 10: 5562 + 618 = 6180
Step 11: 6180 + 618 = 6798
Step 12: 6798 + 618 = 7416
Step 13: 7416 + 618 = 8034
Step 14: 8034 + 618 = 8652
Step 15: 8652 + 618 = 9270
Step 16: 9270 + 618 = 9888
Step 17: 9888 + 618 = 10506
Step 18: 10506 + 618 = 11124
Step 19: 11124 + 618 = 11742
Step 20: 11742 + 618 = 12360
Step 21: 12360 + 618 = 12978

So, 618*21 = 12978